The present disclosure relates to manufacturing tooling, in general, and in particular, to apparatus and methods for trimming the ends of stiffeners disposed on composite skin panels.
Composite aircraft structures promise several benefits for the commercial aircraft industry, including airframes that are both substantially lighter and/or stronger than their aluminum predecessors. Several design considerations are critical to a successful, safe composite aircraft structure design. Two of these, impact resistance and damage tolerance, are critical driving factors for structure weight and cost. Because of these two design requirements, composite fuselage skin structures utilize a minimum gage, or thickness, that is thicker than that actually needed for carrying gross vehicle design loads.
It is known that, by adding elongated stiffening elements to composite skin panels, the panel skin thicknesses can be reduced without reducing panel strength and rigidity. In general, closed “hat” stiffeners provide great torsional rigidity, bending stiffness, and buckling resistance in composite structures for many aircraft applications, such as fuselages. Hat-stiffened composite structures thus typically result in lighter structural weight with less material and manufacturing cost.
One issue with these types of stiffeners is that their as-cured ends need to be “cleaned-up,” i.e., trimmed uniformly to size, after curing. Trimming composite parts is not new, but one problem with skin stiffening elements such as hat stiffeners is that often they do not extend out to the edge of the skins, where trimming of their ends flush with the skin edge would be relatively easy, but instead, terminate within the part boundary. This also results in the hat end interfacing in some way with the inside surface of the skin plies themselves.
The current method for effecting such trimming is to grind or cut the ends of the stiffeners away by hand, yielding a less-than-desirable control of shape and size, with some danger of damage to the underlying skin, and a substantial consumption of time and labor.
Thus, there is a long-felt but as yet unsatisfied need for a fast, reliable tool that enables the end of the hat-shaped stiffeners of composite skin panels to be trimmed at a specific location, with a uniform, desired end shape, and without damaging underlying skin plies.